1. Field of the Invention
The present invention relates generally to reagents, additives, resin blends and the like, that promote degradability in plastics, and more specifically it relates to a reagent that controllably initiates degradability in a specific time frame and reduces toxicity commonly associated with degradable reagents and the like.
2. Background Art
It is clear and apparent that degradable plastic products are becoming more and more in demand with the considerable environmental concerns and public demands of society. As outlined in my co-pending patent application entitled Starch Based Reactor, Resultant Products, and Methods and Processes Thereof, plastic waste is not only filling up landfills at an alarming rate, but is frequently finding a final graveyard in several swirling pockets in the oceans, some considered of major proportions. The quest to find a solution to deal with plastic waste depends on the particular plastic being used and the type of product being manufactured. For example, disposable products such as merchandise bags or disposable plates and containers used in fast food restaurants would tend to require a degradation rate much faster than other plastic products such as toys, office products, home decorations and so on. It is easy to understand that different degradable solutions are needed for the various types of products, depending on the desired rate of degradation.
One approach to making a plastic product degrade at a more rapid rate is the application of blending a degradable reagent into polyethylene and other plastic resins in order to cause them to degrade or biodegrade as the case may be. Some of these plastic products may also be compostable. Starch based resins are also commonly used with certain products and provide excellent compostability, but tend to create low strength films, have poor clarity, and are usually used in applications where recycling is not considered necessary. Due to poor strength issues, films must be substantially thicker, thus the costs are relatively high compared to standard resins, and not considered viable for mass market products. Thus mass market film and container products are manufactured from more inexpensive light gauge films, typically made from virgin ethylene-based resins. For example, bag products may be as thin as 0.0005 gauge, which is not possible to manufacture such a thin gauge with starch based resins.
Another approach to degradable resins involves the use of synthetic aliphatic polyesters Polycaprolactones (PCL) and their associated blends. They tend to provide good compostability, but likewise, strength properties are poor, their cost is high, and recycling is not desirable. Polyhydroalkanoates (PHA) and the related PHB and PHBV provide good compostability, but share the same high cost, inability to be recycled, are difficult to process, and have an unpleasant odor. Its use is primarily limited to certain types of bottles and medical applications. Another aliphatic synthetic polyester is PLA, which has good transparency qualities, is referred to as being “biocompatible” (a somewhat nebulous term depending on a company's definition) but shares the same high cost, poor processability, with a generally more rigid resultant product and is not considered desirable to recyclable. Thus, these types of degradable resins have limited market appeal.
The more popular form of degradable reagent used today are the oxodegradables, which are typically a form of salt that promotes degradability in a plastic by accelerating oxidation of the polymers. Oxygen naturally wants to break down molecular chains, but due to the long molecular chains it takes about 1000 years to break down ethylene-based polymers. Oxodegradables may reduce that time frame down to a few years or even a few months. These prior art reagents consist of a calcium salt, which when added to standard polyethylene (or other plastic resin types) will cause a reaction with the plastic composition that creates an oxygen mass that breaks down the long molecular chains, providing shorter degradable molecules which bio-organisms may consume. This is accomplished through oxidation of the smaller molecules, which transforms for example, a hydrophobic plastic film into hydrophilic film. The result is a bio assimilation film that degrades rapidly. Products made from this type of master batch may degrade at a more rapid rate. These types of reagents are added to polyethylene resins and the like, in relatively small concentrations, whereas the reagent tends to migrate throughout the plastic material when buried, such as in a landfill, and degrade in a relatively short time frame. For example, typical plastic made with an ethylene feedstock will thus degrade in 1000 years in the ground. In comparison those with an oxodegradable additive may degrade in a several months or a few years.
Typical oxodegradables using cadmium salt include those made by Willow Ridge, EPI®, and Symphony Plastics (D2W™). As the case may be, these additives tend to have lower costs than products made with the synthetic aliphatic and starch resins and tend to have superior strength qualities especially when used in products requiring higher strength, such as film. They also tend to be easier to process, and reportedly degrade as litter (in the air) and in the soil, such as in a landfill, and in water if accidently disposed. However, they are slow to compost, i.e. it may take up to 8-10 months or a few years. The cost of these reagents is in generally the $3.20 to $5.00 per pound range.
Reportedly, prior art oxodegradables may be used for a variety of plastics to promote degradability. However, it hasn't been widely applied outside of film products and very little actual testing and verification of degradability results has been performed. The primary reason for the inadequate, unreliable testing is due to the many variables associated with the manufacture of the products using cadmium based salt additives. This conundrum is verified by a report from the United Kingdom government. The 2010 UK government DEFRA report on oxo-biodegradable plastics (OBP) concluded that OBP claims made by one supplier, EPI, were inaccurate and misleading. It was further supported by a leading UK retailer, Tesco, that stopped using and specifying OBP bags due to manufacturing problems, such as trying to maintain bubble stability of the extruded film used in its products.
With the cadmium salt based oxodegradable reagents, degradation may be as fast as 12 to 36 months based on the desired degradation rate of a product, and thus it depends on a specific amount of additive to be used. At times, it takes a longer period of time to degrade if the amount of oxodegradable reagent blended in the resin fails to achieve necessary ratios. This is all due to the fact that control over the percentage added to the resin may vary from batch to batch and even from day to day. The conditions causing these variables in the degradation time frame include: inconsistent blending methodologies; inconsistent monitoring of the injection of additives in the resins; the reduction of the amount of additive blended into the resin batch in order to reduce raw material costs, and suppliers' inability to assess the amount of additive needed to achieve intended degradation times.
Due to the difficulties of properly blending and applying the prior art oxodegradable additives, which is typically blended at a 1%-2% rate, the ultimate degradable outcome tends to be unpredictable. Products made from the master batched resins may contain portions that degrade in a few years, yet other portions may literally take decades or centuries to degrade. Thus, much of the outcome is based on guesswork.
In order for the cadmium salt based additives to be effective, they must be consistently blended throughout the master batch, monitored throughout, and accurately verified that the correct percentages are being used. It is difficult enough to control adding a small percentage of additive let alone ensure that it has produced an amalgamous master batch. Perhaps one of the most compelling factors in the use, or “inadequate use” as the case may be, of the oxodegradable additives, is the cost. Since it costs up to five times more than the resin itself, it adds substantially to the cost of the product being manufactured. This creates a generally unsatisfactory situation, in particular when attempting to maintain competitive pricing. For example, one supplier may have a fairly significant cost advantage over another supplier by reducing the amount of additive used from 2% down to 1% or even 1.5%. Likewise, the potential harm this does when the products hit the landfill, a river, or ocean, becomes detrimental to the environment.
Another approach to satisfying the demands of industry to use degradable resins is the use of a starch based resin as disclosed in my co-pending patent application. For example, products made from the Tapioca based resins will in fact degrade in their entirety in a matter of months, or years in some far reaching scenarios. While this may be an excellent solution in many cases and is competitive cost-wise, the resins are not capable of being used in certain products, such as very thin films or those that may require exceptional strength qualities.
An additive that overcomes the numerous problems associated with prior art degradable reagents and additives would be valuable to these trades and many others.